The Royal Navy joins the EuroPride parade along Oxford Street, London, in 2006, six years after the ban on openly lesbian and gay personnel was lifted. Photograph: Scott Barbour/Getty Images

In the week that the armed forces' LGBT conference takes place in London, Chris Root, a former soldier, still has painful memories of being thrown out of the army for being a lesbian.

When Root joined up in 1970, aged 17, she could not have imagined that she would be discharged just before she completed her four years in the Royal Army Armoured Corps with "services no longer required" stamped on her papers.

"When I joined up I was away from the influences of men and the pressure to conform to heterosexuality. I soon experienced a different world," said Root. "One where lesbian relationships were accepted amongst the other female soldiers."

For the first time, the conference includes not only the LGBT community, but also the military's leaders, policy makers and welfare officers.

Before the law was overturned by the European court of human rights, it was illegal to be openly gay or lesbian in the armed forces. Today, according to the gay rights pressure group Stonewall, the RAF and Royal Navy are among the 100 most gay-friendly employers.

Root, a radar operator, began having sexual relationships with other female soldiers soon after joining up but was quickly made aware that discovery would result in investigation by the Special Investigations Branch (SIB).

"Everyone was terrified of the SIB," said Root, who had begun to suspect that she was being scrutinised under the "McCarthy-like regime". Unable to cope with the pressure, Root handed herself in to the SIB 100 days before her four years were up. "The dread of having my personal possessions raked through and my friends questioned became unbearable."

Root says that other women under suspicion were dragged out of bed in the middle of the night, made to put on full dress uniform, and interrogated for days.

"You would be asked to grass up other women and to disclose intimate details of your sex life. They would break you down until you did not know who you were.

"I had seen it happen to other women. But I could never have imagined how bad it was for me. Those remaining days felt like 100 years."

Today, according to Stonewall, up to 14,000 service personnel are lesbian or gay. The military now advertises for recruits in gay magazines and newspapers.

A survey conducted by the website Proud2Serve, which supports gay service personnel, found that two-thirds of respondents were open about their sexuality to their comrades.

Major Damian Jenkins, chair of the army LGBT forum and one of the organisers of Friday's conference, said: "This change reflects the recognition of commanding officers of the benefits of a diverse workforce, and a desire to be more inclusive.

"The audience will range from the most junior ranks to senior generals. Between us we hope to identify ways in which the military can continue to keep pace with the liberal society that it serves.."

Linda Riley, founder of the European Diversity Awards, which named Proud2Serve the outstanding employee network group of the year, will speak at the conference about positive lesbian role models. "I wanted to join the army when I was younger but did not because it used to be illegal to be gay in the armed forces, and I have never been a very good closet gay.

"I never thought that things would move on so much that the military would hold an LGBT conference."

Mandy McBain, a former lieutenant-commander who now works for Stonewall, joined the navy in 1986 but was not out as a lesbian until the law was repealed. In 2008 she set up a support group for lesbians and gay men that is backed by the Admiralty. "We still have a long way to go, but if there is discrimination then those affected have other places to go and seek help, such as the LGBT forums or Proud2Serve. There are increasingly robust procedures in place."

Lance Corporal James Wharton, a trooper in the Household Cavalry, was one of the first openly gay men in the army and in 2009 appeared on the front cover of Soldier magazine.

Wharton came out in 2005 at the age of 18, two years after joining the army. "It is amazing how much the army has changed in a relatively short space of time," he said. "Gay soldiers now not only feel tolerated, but celebrated."

As recently as 1999, one year before the law changed, 298 lesbians and gay men were dismissed from the army alone.

Root, today an equality and diversity expert on workplace discrimination, says that more than 40 years on, the scars from her experiences of going through what she describes as a "homophobic witch-hunt" still remain.

"Being thrown out of the army affected my career for a number of years because I felt so lost. If I had left under normal circumstances I would have had job training and been otherwise rehabilitated back into civilian life. But instead, despite what I had given to my country, I was dumped as though I was worthless."